1. Field of the Invention
The present invention relates to a method for manufacturing a polyester fiber cord that is treated with an adhesive and used for reinforcing rubber products, such as tires, hoses, conveyor belts, V belts, power transmission belts, rubber containers, and the like.
2. Description of the Prior Art
Polyester fibers are superior in mechanical properties, dimensional stability, and durability, and they are widely used not only for garments usage but also for industrial usage and for reinforcing rubber materials, such as tire cords, V belts, conveyor belts, hoses, and the like. However, in comparison with nylon fibers, they have a drawback that their adhesive property to rubber materials is decreased; in particular, when they are embedded into rubber compounds and are exposed to high temperatures for a long period of time, their adhesion strength is remarkably deteriorated. It has been considered that decrease in adhesive strength of a polyester fiber in rubber compounds is caused by degradation of the polyester fiber due to action of amines and water contained in the rubber compounds, and many proposals have been given in order to overcome this drawback.
On the other hand, for using a cord in V belts, in some cases, a cord is cut in a longitudinal direction when it is embedded in rubber materials to be molded into a belt. Then, cohesiveness of the cord itself is also an important property. However, heretofore, in order to give such a property, the cord needs to be treated with a polyisocyanate in the presence of an organic solvent, or the like. For example, JP 51-70394 A discloses a method in which a polyester fiber containing no more than 10 μeq/g of carboxyl terminal groups is subjected to treatment with an epoxy compound as well as treatment with a polyisocyanate compound and treatment with a resorcine formaldehyde latex (RFL). However, the method is impractical because the polyisocyanate treatment is carried out in an organic solvent system, and the method is of three-stage dipping treatment.
Further, since this organic solvent has high environmental burdens, a recovery step is required, and protection measure for healthy maintenance of workers is also required, leading to decrease in workability. Furthermore, in this method, since a device having explosion-proof construction is required for the treatment, a large-scale device is needed, which causes disadvantage in cost.
As an example of a system in which an organic solvent is not used, JP 60-31950 B discloses a method for manufacturing a polyester fiber wherein treatment with a liquid comprising a carrier is carried out at least prior to treatment with an adhesive, and thereby obtaining a polyester fiber material demonstrating little decrease in adhesive strength at the time of being exposed to high temperatures in rubber materials for a long period of time, and the method demonstrates some effect in a heat-resistant adhesive property. However, the method has a problem of deterioration of strength and fatigue resistance.
Furthermore, JP 2000-8280 A discloses a method for manufacturing a polyester fiber material for reinforcing rubber materials, wherein a fiber cord is treated with a treating liquid comprising a carrier, an aqueous solution of blocked isocyanate, a dispersion of epoxy resin, and a resorcin-formaldehyde latex mixture, and thereby obtaining a polyester fiber having a remarkably improved heat-resistant adhesive property at the time of being exposed to high temperatures for a long period of time in a state where the fiber cord is embedded in rubber compounds. In this method, since the carrier contained in the processing liquid is considered to have a high burden to environment, the method is not practically preferable.